The invention relates to microlayer films microfibrillated to bear a fibrous surface, methods of preparing them, and articles made from them.
Polymeric materials that can be processed to form microfiber surfaces and microfiber articles have been identified, including mono-axially oriented films such as polypropylene. See U.S. Pat. No. 6,110,588. Such polymeric materials can be selected and processed using various techniques, to produce oriented films capable of being microfibrillated to a microfiber surface.
Microlayer films are generally known, and include a variety of different combinations of layer composition, sizes, and methods of preparing the different layers into a microlayer film, and are generally known for their specialized optical properties.
Until now, there has been no recognition of the benefits that can be achieved using co-extruded microlayer films to form microfibers, microfiber surfaces, and microfiber articles.
The invention identifies microlayer films that can be microfibrillated to bear very fine fibers, e.g., microfibers, methods of preparing the films and forming them into fiber-bearing articles, e.g., microfiber articles, and the fiber bearing articles so prepared. The films and their derivatives are referred to as microfiber-articles.
The invention specifically contemplates that certain oriented microlayer films can be fibrillated to form fibers, especially microfibers. (The descriptions herein highlight the invention with respect to xe2x80x9cmicrofibrillationxe2x80x9d and the formation of xe2x80x9cmicrofibersxe2x80x9d and xe2x80x9cmicrofiber products,xe2x80x9d but the invention is not limited to the formation of microfibers or fibers of any size limitation; and one of skill will be able to understand that where the words microfibrillate, microfiber, or microfiber products are used, one could instead practice the invention to fibrillate, to form a fiber or fibrous surface, or a fiber or fibrous product.) While wishing not to be bound by theory, it is believed that interfaces between individual layers of oriented microlayer films can be sufficiently weak that the microlayer film can be fibrillated, sometimes relatively easily, to form a fibrous surface, preferably microfibers. Some films can be microfibrillated after orienting to a draw ratio of as little as about 6:1 or even 3:1. This is much lower than the xcx9c10:1 draw ratio typically needed to microfibrillate monolayer polypropylene with fluid energy. In this same respect, it has been found that some polymer layers that heretofore could not be processed to produce microfibers can be included in uni-axially oriented microlayer films that will produce microfibers from those polymers, e.g., polystyrene. Microfibrillation of certain polymer layers of microlayer films can in some instances be realized even absent substantial molecular orientation in the microlayer film typically needed for microfiber formation. Easier fibrillation, e.g., in the form of reduced energy expenditure, can be accomplished with oriented microlayer films when compared to single layer sheets of similar draw ratio.
According to some preferred embodiments of the invention, uni-axially oriented, microlayer polymeric films can be processed into microfiber articles bearing one or more microfiber surfaces. These microfiber articles may be designed into useful products for a great variety of applications, including as mats or cloth-like materials. General advantages of the microfiber surface include that the extent of fibrillation can be controlled to enhance surface area; the surface glossiness or other optical properties of the surface can be enhanced or modified due to the presence of the microfibers; the microfiber surface of a microfiber article can be used as a reinforcing material in the manufacture of composite materials to enhance interfacial bonding; and microfiber articles can be used in microlayer constructions where the wicking effect of the microfiber surface can enhance adhesion or integrity; and, the soft nature and absorbency of the microfiber surface allows the manufacture of inexpensive wipes or adhesive bandages. In other applications, the invention can be applied to membranes, filters, or devices where materials include a fibrous or a porous surface. A separate advantage includes the possibility of easily handling small fibers in large volumes without separating them from the main web. Also, the films can have enhanced electrical chargeability or charge retention, even beyond that already retained by a fibrous highly oriented polymer. Fibrous articles can be prepared with an enhanced bulkiness due to small fiber diameters that are not self collapsing but stiff, and by selecting a high modulus starting material.
The microlayer films can be formed to a fibrous, e.g., microfiber, surface using standard methods of fibrillation, including hydroentanglement techniques using a hydroentangling machine. The depth of fibrillation of a microfiber-forming layer, or the number of layers transformed, can depend on the extent of fibrillation, which with hydroentangling processes can depend on, e.g., the amount of time that a film spends under a fluid jet of a hydroentangling machine, the intensity to which the fluid strikes the sample, the polymer properties, and to a lesser extent, the fluid and material temperature. For the microlayer films described herein, one or more of the layers maybe microfibrillated to form microfibers, and where two microfiber forming layers are adjacent to each other, microfibrillation can penetrate fully through one layer causing microfibrillation of the adjacent layer and entanglement of the microfibers of the adjacent layers. Also optionally, microfibrillation may penetrate two or more layers, e.g., adjacent layers of a microlayer film, or microfibrillation may penetrate the entire thickness of the film. By microfibrillating two or more layers of a film, microfibers can be formed from more than a single layer. Microfibers from the different layers can be present at a microfiber surface of a microfiber article, and can provide different properties if desired.
Thus, in some respects, the invention recognizes that certain processing techniques and compositions of microlayer films, especially co-extruded, mono-axially oriented microlayer films, can facilitate fibrillation or microfibrillation of polymer layers of such microlayer films, or even make microfibrillation possible for polymeric layers that cannot otherwise be microfibrillated.
In some other respects, the invention takes advantage of the understanding that films having multiple different layers with independently selected properties can be formed into a microlayer film and then microfibrillated to efficiently produce a microfiber article having a desired combination of properties based on the composition and properties of the different layers of the film. Thus, different layers of a microlayer film can advantageously be selected to include one or a variety of different properties, optionally to produce a microfiber article having a combination of desired properties. For example, different layers of a microlayer film can be independently selected to provide layers that are one or more of hydrophobic; hydrophilic; oleophobic; oleophilic; dielectric; to exhibit a certain mechanical property such as rigidity, flexibility, high or low elasticity, or high or low strength; stain resistance; to give a desired frictional property such as a high or low coefficient of friction; to provide a desired color or color combination; to provide a desired size of microfibers or a desired surface area of a microfiber surface; or combinations thereof.
As a particular example, one layer can be selected to be a hydrophilic material, to provide hydrophilic microfibers, while another layer may be oleophilic. As a different example, a fiber mat could be produced with both PP and PET fibers in one step. The PP fibers would be good for insulation, while the stiffer PET fibers could provide loft to the fiber mat. In this same manner, other layers of microlayer films can be selected to have layers of various properties which when microfibrillated can produce various multi-surface articles such as pads, drapes, cloth-like wipes, microfiber mats, and a large variety of others, which contain two or more different types of materials, optionally with two or more different types of microfibers.
Also, microlayers of a microlayer film can be selected to include one or more microfiber-forming layer and one or more layer that is not a microfiber-forming layer, e.g., to give a combination of properties from the different layers, or to form fibers that are larger than microfibers. The non-microfiber-forming layer can be selected to give a certain property, such as hydrophobicity, hydrophilicity, breathability, etc., for its stain or water resistance, or a mechanical property such as support, rigidity, flexibility, strength, or elasticity. As an example, a co-extruded microlayer film can have an inner layer of a plastic, a fluoropolymer, a flexible or soft rubber, an elastomer, etc. The microfiber article may exhibit a combination of properties including properties of a waterproof elastomer and properties of microfiber surfaces, to give an article having combined properties of a flexible or stretchable microfiber-surface-bearing cloth. As another example, a durable and strong non-microfibrillating layer can make it easier to handle a microfiber film in the form of a web, eliminating the need for a separate supporting web.
The invention allows fibrillating one or two surfaces of a co-extruded microlayer film. A patterned microfiber surface is also possible.
An aspect of the invention relates to an oriented microlayer film, microfibrillated to produce microfibers.
Another aspect of the invention relates to a co-extruded, uni-axially oriented microlayer film that can be microfibrillated to produce microfibers.
Another aspect of the invention relates to a microfiber article comprising a co-extruded, uni-axially oriented microlayer film comprising microfibers.
Another aspect of the invention relates to a method of producing a microfiber article. The method includes co-extruding a microlayer film comprising at least one layer that can be oriented into a microfiber-forming layer, orienting the at least one layer into a microfiber-forming layer, and microfibrillating the microfiber-forming layer to form microfibers.
Yet another aspect of the invention relates to an oriented microlayer film, fibrillated to produce fibers from at least one layer of the microlayer film.
Yet another aspect of the invention relates to an oriented microlayer film, fibrillated to produce a fibrous surface.
Yet another aspect of the invention relates to a method of producing a fibrous article. The method includes co-extruding a microlayer film comprising at least one layer that can be oriented into a fiber-forming layer, orienting the at least one layer into a fiber-forming layer, and fibrillating the fiber-forming layer to form fibers.